Layered decoding architecture with reduced number of hardware buffers for LDPC codes

Abstract

A layered decoding architecture with a reduced number of hardware buffers for low-density parity-check (LDPC) decoding by storing a variable-to-check message. When a check node begins a new operation, a variable-to-check message (Q) is added to a check-to-variable message (R) obtained in previous check-node operation to obtain an updated APP value. Then, the R value for the check node in the layer being processed is deducted from the APP value to obtain a variable-to-check message (Q). This variable-to-check message is stored in the memory and inserted into the check node equation to obtain a check-to-variable message. Finally the check-to-variable message obtained in this operation is stored to the check-to-variable message shift register to complete the updating operation for the check node and the variable node for the layer being processed. Improved hardware utilization and fewer buffers, thus achieving a smaller hardware area while retaining the converge speed, is obtained.

What is claimed is: 
     
       1. A layered decoding architecture for low density parity check (LDPC) decoding comprising:
 a variable-to-check message magnitude memory configured to store obtained magnitudes of channel values as initial or later calculated variable-to-check message magnitudes; 
 an A Posteriori Probability (APP) calculation unit electrically coupled to the variable-to-check message magnitude memory and configured to sum a variable-to-check message (Q) and a check-to-variable message (R), APP=Q+R; 
 an APP sign routing network unit electrically connected to the APP calculation unit so as to route updated APP signs to each corresponding variable node; 
 an APP sign memory electrically connected to the APP sign routing network unit so as to retrieve routed and updated APP signs; 
 an APP routing network unit electrically connected to the APP calculation unit so as to route updated APP values to corresponding check nodes; 
 a variable-to-check message calculation unit electrically connected to the APP routing network unit; 
 a variable-to-check message sign memory electrically connected to the APP calculation unit and to the variable-to-check message calculation unit so as to provide corresponding stored variable-to-check message signs and store variable-to-check message signs obtained from the variable-to-check message calculation unit; and 
 a check-node processor electrically connected to the APP calculation unit and to the variable-to-check message calculation unit, 
 wherein the APP calculation unit updates the APP values for all related variable nodes j connected to the check nodes i in the check-node layer being processed after all these variable nodes j are updated according to the following APP equation:
     APP   j   =Q   f(i,j)j   +R   f(i,j)j   , ∀jεN ( i ) 
 
 where f (i, j) represents the check node which performs the final check-to-variable message delivery together with the variable node j prior to the check node i being processed, Q f(i,j)j  and R f(i,j)j  are, respectively, the variable-to-check message and the check-to-variable message corresponding to check node f (i, j) and variable node j. 
 
     
     
       2. The architecture of  claim 1 , wherein the variable-to-check message is the combination of the variable-to-check message magnitude and the variable-to-check message sign and wherein the check-to-variable message is the combination of the check-to-variable message sign equal to a product of the total product of the variable-to-check message signs, the variable-to-check message signs, and the check-to-variable message magnitude which is calculated using a minimal variable-to-check message index and minimal and second minimal variable-to-check message magnitudes. 
     
     
       3. The architecture of  claim 1 , wherein the variable-to-check message calculation unit retrieves the routed APP value, the variable-to-check message sign and a total product of the variable-to-check message signs, a minimal variable-to-check message magnitude index, and a minimal and second minimal variable-to-check message magnitudes and then calculates the variable-to-check message by subtracting the check-to-variable message from the routed APP value, Q=APP−R. 
     
     
       4. The architecture of  claim 3 , wherein the check-to-variable message is a combination of the check-to-variable message sign, which is a product of the total product of the variable-to-check message sign and the variable-to-check message sign and the check-to-variable message magnitude which is calculated using the minimal variable-to-check message index and the minimal and the second minimal variable-to-check message magnitudes such that the variable-to-check message calculation unit calculates the variable-to-check message using both the routed APP value and the check-to-variable message. 
     
     
       5. The architecture of  claim 1 , wherein the calculated variable-to-check message and sign and magnitude thereof as stored in the variable-to-check message sign memory and the variable-to-check message magnitude memory, respectively, are then combined and then simultaneously forwarded to the check node processor. 
     
     
       6. A layered decoding architecture for low density parity check (LDPC) decoding comprising:
 a variable-to-check message magnitude memory configured to store obtained magnitudes of channel values as initial or later calculated variable-to-check message magnitudes; 
 an A Posteriori Probability (APP) calculation unit electrically coupled to the variable-to-check message magnitude memory and configured to sum a variable-to-check message (Q) and a check-to-variable message (R), APP=Q+R; 
 an APP sign routing network unit electrically connected to the APP calculation unit so as to route updated APP signs to each corresponding variable node; 
 an APP sign memory electrically connected to the APP sign routing network unit so as to retrieve routed and updated APP signs; 
 an APP routing network unit electrically connected to the APP calculation unit so as to route updated APP values to corresponding check nodes; 
 a variable-to-check message calculation unit electrically connected to the APP routing network unit; 
 a variable-to-check message sign memory electrically connected to the APP calculation unit and to the variable-to-check message calculation unit so as to provide corresponding stored variable-to-check message signs and store variable-to-check message signs obtained from the variable-to-check message calculation unit; and 
 a check-node processor electrically connected to the APP calculation unit and to the variable-to-check message calculation unit, 
 wherein the variable-to-check message calculation, unit produces the variable-to-check message Q ij  for variable node j related to all the check nodes i in the check-node layer being processed using the following variable-to-check message equation,
     Q   ij   =APP   j   −R   ij   , ∀jεN ( i ) 
 
 
       where APP j  represents the APP value updated in the previous operation for variable node j; and R ij  represents the check-to-variable message from check node i to variable node j obtained in the previous decoding iteration. 
     
     
       7. A layered decoding architecture for low density parity check (LDPC) decoding comprising:
 a variable-to-check message magnitude memory configured to store obtained magnitudes of channel values as initial or later calculated variable-to-check message magnitudes; 
 an A Posteriori Probability (APP) calculation unit electrically coupled to the variable-to-check message magnitude memory and configured to sum a variable-to-check message (Q) and a check-to-variable message (R), APP=Q+R; 
 an APP sign routing network unit electrically connected to the APP calculation unit so as to route updated APP signs to each corresponding variable node; 
 an APP sign memory electrically connected to the APP sign routing network unit so as to retrieve routed and updated APP signs; 
 an APP routing network unit electrically connected to the APP calculation unit so as to route updated APP values to corresponding check nodes; 
 a variable-to-check, message calculation unit electrically connected to the APP routing network unit; 
 a variable-to-check message sign memory electrically connected to the APP calculation unit and to the variable-to-check message calculation unit so as to provide corresponding stored variable-to-check message signs and store variable-to-check message signs obtained from the variable-to-check message calculation unit; and 
 a check-node processor electrically connected to the APP calculation unit and to the variable-to-check message calculation unit, 
 wherein the check node processor performs the check-to-variable message calculation according to the following check node equation related to all the check nodes i′ in the check-node layer being processed:
     R   i′j =α└Π kεN(i′)/{j} sign( Q   i′k )┘min kεN(i′)/{j}   {|Q   i′k   |}, ∀jεN ( i ′)
 
 
 
       where α is the normalization factor, └Π kεN(i′)/{j} sign( Q   i′k )┘is the product of the variable-to-check messages signs that are forwarded from the variable nodes connected to the check nodes i′, except for the variable node j, min kεN(i′)/{j}   {|Q   i′k |} is the minimal variable-to-check message magnitude held by one of the variable nodes in set N(i′) except for the variable node j; and thereby the check-to-variable message R i′j  from check node i′ to variable node j is obtained.